Control potentiometer



1958 J. GlUFFRlDA ET AL 2,856,124

CONTROL POTENTIOMETER Filed NOV. 30, 1954 INVENTORS Joseph Giuffridcl y Guy B. Prurio Jr.

ATTORNEY CONTROL POTENTIOMETER Joseph Giutfrida, Peabody, and Guy B. Praria, Jr., Salem, Mass, assignors to Columbia Broadcasting System, Inc., Danvers, Mass, a corporation of New York Application November 30, 1954, Serial No. 472,080

7 Claims. (Cl. 315-13) This invention relates in general to balanced electronic circuits and in particular to relative color brightness adjustments in color television.

In present day color television receivers, it is the practice to use a tricolor tube. The commoner types of color tubes depend for their operation on the phosphors of which the screen is composed emanating red, green and blue light upon excitation by electron beams. It is desirable, if not necessary, at the present point of development of color television that the receiver be capable of producing a black-and-white picture as well as a color picture. Because the elficiencies of phosphors are not equal, it is not possible merely to run the red, green and blue phosphors simultaneously and depend upon the output to be a pure white by reason of the mixture of the three colors. It is necessary that some provision be made for varying the relative brightness of light of the three colors to obtain an acceptable white.

It has been the practice in those tubes which utilize three guns to provide a bias potentiometer for the control grid of each gun in order that the intensity of the beam from each gun be individually adjustable. These controls are usually set in the factory when the beams are properly balanced. Because of the difficulty involved in adjustment, not the least of which is inter-action with screen grid controls and drive adjustment controls in' each gun, it has not been advisable to leave to the set owner the rather intricate problem of obtaining so-called white balance. Unfortunately, aging of tubes and other components in the receiver circuit requires that white balance be reset occasionally as the set is used. The set owner is then placed in the dilemma of having an unsatisfactory picture or paying for the services of a repair man to make the necessary re-adjustments.

A further complication in the adjustment of white balance is that the acuity of the human eye to each of the primary colors used in the tri-color tubes varies from person to person. This fact makes perfect factory adjustment of white balance for every set owner impossible. Therefore, statistical standards are used to adjust white balance so that the factory adjustment is most pleasing to the greatest number of persons. While such statistical standards allow mass production to be carried on in an economical manner, any person whose eyes differ appreciably from the established norm sees an ap parently misadjusted tri-color picture.

Even a person having some skill in making such adjustments is handicapped by the fact that the process of adjusting the relative brightness of each of the primary colors is of the cut-and-try variety in that it is necessary to make a series of approximations wherein one, then the second and, finally, the third potentiometer is adjusted to balance the primary colors one against the others. It is obvious that, even with skilled technicians, time is consumed and money expended to obtain a satisfactory picture. It is equally obvious that if color television receivers are to be within the reach of the mass market, reductions in complexity and in cost of cornnit Sttes atent O 2,856,124 Patented Dec. 23, 1958 ice ponents must be introduced. Furthermore, the color receiver should be developed to the point where the owner is able to make necessary minor adjustments to maintain good results. Any device which constitutes even a partial solution to these general problems as well as a full solution to the specific problem of adjustment of color balance would constitute a considerable advance in the color television art.

Therefore, it is an object of the present invention to lessen the cost of manufacture by reducing the number of components required to accomplish the required control of relative color brightness.

Another object of the present invention is to simplify the'techniques presently employed to obtain the required relative color brightness so that even unskilled individuals may adjust for white balance.

A further object of this invention is to provide a pleasing picture to those persons whose subjective reaction to light of varying hues differs from the reaction of the person with normal eyes.

A still further object is to provide a novel potentiometer for general use.

In general, this invention consists of a homogeneous resistive element which may be applied to a spherical surface. A voltage may be applied through a pivotally mounted contact arm to any selected point of the surface. The pivot point of the arm is preferably coincident with the center of curvature of the spherical surface. Contact points are provided as desired on the resistive element. It is evident that the voltage drop from the movable arm to any of the fixed contacts through the resistive element can, in a simple embodiment, be made a function of distance therebetween so that the voltage drops from the movable contact to each of the :fixed contacts may be changed simultaneously as required. For a better understanding of the invention together with other and further objects, features, and advantages, reference should be made to the following description which is to be read in connection with the accompanying drawing in which:

Fig. 1 is an exploded perspective view of an embodiment of this invention;

Fig. 2 is a partial cross-section of an embodiment of this invention to show how contact may be made to the resistive material; and

Fig. 3 is a schematic diagram of an embodiment of this invention as used in a tri-color circuit.

Referring to Fig. l, the homogeneous resistive element 1 is shown on a hemispherical surface formed on the inside of a supporting base 3. Electrical contacts 2 are secured around the periphery of the resistive element 1. A flexible conductive membrane 4 which is hemispherical in shape is concentrically mounted on the supporting base tact 6 is also shown as an integral part of the conductive membrane 4. A cover plate 7 rests on top of the flange '5. Circumferentially disposed screws 8 secure the base support 3, the flange 5 of the hemispherically shaped membrane 4 and the cover 7 so that relative motion between these parts is not possible. An arm 9 is mounted in a universal joint 10 in the center of cover plate 7. Before assembly of the cover plate 7 to the base plate 3 and the flange 5 of the conductive membrane 4, a retaining ring 11 prevents arm 9 from falling out of universal joint 10. The length of arm 9 below the cover plate 7 is substantially greater than the radius of curvature of the conductive membrane 4, but less than the radius of curvature of the resistive material 1. When the cover plate 7 carrying the arm 9 is assembled to the base plate 3 and the flange 5 of the conductive membrane 4, the membrane 4 is deformed as at the point 12 so that the conductive by arm 9. It will be noted that frictional forces pre nt at the bearing points on arm hold arm 9 in any desired position and ensure a'good electrical contact between t he conductive membrane 4 and the resistive element 1.

a It should also be noted that the position of the point of deformation 12 of the conductive membrane 4, as illustrated, is only one of an infinite number of possible positions. I 7 fig. 3 isa schematic drawing of the electrical circuit with the terminals marked in accordance with Fig. 1.

The circuit shown in solid lines represents a possible ratio of resistances while the circuit shown in broken lines represents'a different ratio which is possible if the contact point on the arm 9 is moved in the direction of the arrow in Fig. 3.

The diagram also indicates the wayiin which the po- 1 tentiometer may be used in a practical white balance circuit. If a common bias source, as labelled, is connected to the conductive membrane 4 throughthe terminal 6, three independent voltage dividers are completed. Each divider may be considered individually to'prove rigorously that the voltage drop from the contact point 12 between the membrane 4 and contact 2 is a function of the distance between the contact point 12 and the contacts 2. By connecting each of the guns ina tri-color tube to each of the contact points 2 on the embodiment of the invention 'as' shown, it is obvious that the bias on each of the guns is also a .of the distance between each ofthe contact points 2 on the periphery of the resistive material 1 and the Qcontact point 12. It is also obvious that the ratio .offthe bias on any pair of guns maybe heldconstant withfresp'ect to each other while changing'with're- :spect to the third'merely by moving point 12 directly toward or away from the third contact point. 'Movement offpoint 12 in any other direction results in changing the ratio of' all three biases simultaneously, each with respect to each other.

In a practical application of the inventiont-o a color receiver, the mounting is simply arranged so that the arm 9 is available for adjustment outside the cabinet. If divided, the cover plate 7 may be incorporated as a part of the cabinet or control panel wall.

' The invention 'hasbeen illustrated and described in connection with one practical potentiometer in which it has 'been incorpo-rated, It is believed that the concept of adjusting independentelectrical variables, the ratio of which must be kept fixed each with each other,with av lcommon means may be applied to many different balanced circuits. It is obvious that the resistivity of the resistive material per unit length may be varied tofobtain ratios which vary in any desiredmanner. ltis equally obvious that the position of the contacts of theiesistive material. may be changed and that standard manufacturing tech niques may be used to vary the materials used in the embodiment specifically described herein. For these reasons, the invention should'be limited only by the scope of the appended claims.

What is claimed is: 1. A potentiometer comprising, a hollow hemispherical supporting base, a homogeneous re'sistive'material attached to the inner surface of said supporting ba'se,"a"plurality of contacts mounted on said base' whereby electrical contact is made at selected points on the periphery offsaid resistive material, a resilient conducting hemispherical contacting membrane concentrically"mountedto saidu porting base, and means deforming any selected portion of said contacting membrane whereby said -contacting 4 membrane touches said resistive material under said deformed portion.

2. A potentiometer comprising, a hollow hemispherical supporting base, a homogeneous resistive material attached to the inner surface of said supporting base, a plurality of contacts mounted on said base whereby electrical contact is made at selectedpoints 'on the periphery of said resistive material, a fiat coveron said supporting base, means attaching said cover to said base, an elongated voltage input arm'pivotally mounted in said cover,-means 'riiakinganelectrical contact between the end of said input arm and said resistive material.

3.;j-A potentiometer comprising, a fiat homogeneous resistive material, means supporting said resistive material. a pluralityofcontacts around the periphery of said resistive material, two elongated arms mounted at right angles to each other and each of said arms having a longitudinalslot and each of-said arms being slidably mounted whereby each of 'said arms is free to move independently at right angles to the other of said arms, an elongated arm supported in the space formed by the intersection of said slots, an electrical contact on the end of'said elongated arm and resiliently contacting said resistive surface.

4. In a 'color television receiver having means for generating red, blue, and green colors, at potentiometer forproviding white balance comprising, a hollow hemispherical supporting base, a resistive material disposed upon. saidbase, three fixed contacts about the periphery length of said resistive material being adjusted to vary in"a."predeterm'ined manner over the area thereof, a "plurality offixed c'o-ntacts'bein'g mounted at predeterrriin'ed' points on' the periphery of said hemispherical base, each of said fixed contacts being in contact with a predetermined point on the periphery of said resistive material, a movable contact, and means for moving said movable contact to any point on the surface of said resistive material.

6. A potentiometer comprising, a hollow hemispherical fSupporting baSe, a resistive material being attached to and completelycovering the inner surface thereof, the thickness of said resistive material being varied in'a predetermined manner, a plurality of electrical contacts 'bieing' afiixed to said supporting base, each ofsaid. electrical contacts making" contactat selected points adjacent the Periphe y bf'jsaid' resistive" material, a resilient" electrical'ly' conductivemembrane being "mounted concentrically "with said supporting base and electrically insulated from said resistive material and said electrical contacts, and means deforming any selected portion of saidmembrane whereby said membrane touches said resistive materialunder said defo'rmed portion.

7. A'potentiometer as described in claim 6 in which said "means deformingany=selected portion of said membrane includes an arm pivotallymounted at'the center *ofcu'rvatureof said-supporting base, afirst part or said arm extending inwardly-toward said'membrane and said hemispherical supporting base, the length of said first part being substantially equalto the radius of curvature saidisupporting base," and a second part of said arm :exterrding' away ro v said rriembrane' and said siipport- "mg base and being" adapted to" allow the'end' of said first part of said arm to be moved to any point on said membrane.

References Cited in the file of this patent UNITED STATES PATENTS 5 Stoekle Nov. 14, 1939 6 Barnett Feb. 18, 1941 Bamford Mar. 2, 1943 Iams May 2, 1944 Amdursky et a1. Sept. 30, 1952 Pokswer Apr. 14, 1953 

